The present invention relates to rotary cone bits, and in particular to a rotary cone bit having a bit body for enhanced cutting removal.
Rotary cone bits are well known in the art of drilling. The most common design of a rolling cone bit consists of three generally conical shaped cutters, each rotatably mounted on a downwardly extending bearing pin. Each of the bearing pins is spaced approximately 120xc2x0 apart with the three pins formed as a part of a bit body. The entire structure is rotated at the end of a drill string. Boring is accomplished by applying weight to the drill bit and rotating the drill string, thereby causing the cutters to roll and crush the rock formation beneath the bit. As the bit is rotated and moves through a formation, the cutter elements contact and disintegrate portions of the formation in order to form the desired bore hole. A large portion of the cuttings produced by the drilling operation are in the form of finely divided particles which create a highly abrasive environment. These cuttings from the bottom and sides of the bore hole are washed away by a drilling fluid, such as air or drill mud, that is supplied to the drill bit from the surface through the hollow rotating drill string. The cuttings are carried to the surface suspended in the drilling fluid.
The grinding and re-grinding of the cuttings produced by the drilling operation slows the formation penetration rate of the bit and shortens the life of the bit. The re-ground cuttings tend to dull the cutters and the finely ground particles are forced into the bearing surfaces formed between the roller cones and the journals supported by the bit, further limiting bit life.
In conventional drill bit construction, the drilling fluid, either drilling mud or air, is directed by nozzles against the cutter cones to wash the cuttings from the cutter cone and the bore hole. Often, the direction of the drilling fluid against the cutter cone results in trapping some of the cuttings along the bottom of the hole with the result that the cuttings are re-ground to an abrasive powder before removal.
Thus, there is a need for an improved rotary cone bit having leg portions configured to enhance chip removal from the bore hole bottom. In addition, there is a need for an improved rotary cone bit having nozzle location and configuration to enhance chip removal from the cutter cones and the bore hole bottom.
In accordance with the present invention, there is provided an improved rotary cone bit having a threaded end for coupling to a drill string and including a drill bit body having two or more leg portions extending from one end of the body. Formed integral with each of the leg portions is a bearing pin that extends inwardly toward the longitudinal axis of the drill bit body. On each of the bearing pins, there is rotatably mounted a cutter cone having rows of cutting teeth as a part thereof. The bit shirttail comprises a plateau extending along the longitudinal axis in substantially the same plane as the bearing pin surface area of the shirttail.
Further, the improved rotary cone bit of the present invention comprises a plateau on each of the leg portions of the bit body. The plateau is part of the shirttail of the leg portion and extends along the longitudinal axis of the bit from the bearing pin surface area to the threaded end. The surface of the plateau extends in substantially the same plane as the bearing pin surface area until a break point at which the plateau tapers to the threaded end. The break point is about between one-third to two-thirds of the length of the plateau from the bearing pin surface area to the threaded end. Further, the improved rotary cone bit of the present invention includes a first contoured surface on the leg portion wherein the first contoured surface is contiguous to the plateau and has a longitudinal axis substantially parallel to the longitudinal axis of the bit body. The first contoured surface is angled down and away from the plateau and extends from the bearing pin surface area to the threaded end. A second contoured surface also formed on the shirttail of the leg portion is contiguous to the plateau and has a longitudinal axis substantially parallel to the longitudinal axis of the bit body. This second contoured surface is angled down and away from the plateau and extends from the bearing pin surface area to the threaded end.